Multi-disciplinary approach to evaluate hydrocarbon potential in the Bornu Basin, Northeastern Nigeria

Abstract

The Bornu Basin, a sub-basin of the Chad Basin in northeastern Nigeria, has experienced extensive petroleum exploration activities, with 23 wells drilled; however, only two encountered sub-commercial gas volumes. This study integrates well log data, sequence and seismic stratigraphy, structural interpretation, and fault seal analysis to better understand reservoir extent, depositional environments, and hydrocarbon trapping mechanisms. Well log analysis reveals a stratigraphic sequence gently dipping from southwest to northeast. The lowermost Bima Formation (Albian), composed mostly of sandstone, reflects a fluvial to continental setting. The Gongila Formation consists of interbedded lithologies, thinning southwestward. The Fika Shale, marked by high gamma ray readings, serves as a thick, continuous seal. The Gombe Formation, with alternating sands and shales, indicates fluvial to shallow marine conditions. The sandy Kerri-Kerri Formation suggests a continental environment, while the Chad Formation comprises clays and shales with minor sandstones. Sequence stratigraphic analysis identified three third-order sequences. Reservoir evaluation in Bulte-1 and Kasade-1 wells identified three potential reservoir zones (Cha-Res-1, -2, -3) in the Kerri-Kerri, Gombe, and Gongila Formations; respectively. The Kerri-Kerri and Gombe Formations show better reservoir quality with good porosity (0.13–0.18) and net to gross (0.93–0.98); respectively, while the Gongila Formation is poorer due to higher shale content (0.150–0.157) and high-water saturation (0.99–1.00). Seismic data revealed complex faulting patterns like normal, listric, and reverse especially in deeper zones, along with possible igneous intrusions. Two anticlinal leads were identified. Fault seal analysis suggests moderate sealing capacity with a Shale Gouge Ratio of 0.22–0.35. Rose diagram, Fisher mean vector statistics and Bingham axial distribution analysis suggest that the faults are trending in Northeast-southwest direction.